Use arm_eabi_breakpoint on aarch32

Use arm_eabi_breakpoint on aarch32

Nowdays, GDBserver chooses arm breakpoint instructions by checking
macro __ARM_EABI__.  When aarch64 GDBserver debugs arm program,
arm_eabi_breakpoint is still needed, but __ARM_EABI__ isn't defined
in aarch64 compiler.  This causes GDBserver chooses the wrong
breakpoint instruction for arm program.  This patch fixes it.

gdb/gdbserver:

2015-12-11  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch32-low.c [__aarch64__]: Use arm_abi_breakpoint
	arm breakpoint.